1. Field of the Invention
The present invention relates generally to a multi-mode mobile station and, more particularly, to an efficient handover processing method and system for a multi-mode mobile station capable of supporting unlicensed mobile access (UMA) technology.
2. Description of the Related Art
In general, licensed wireless systems (mobile communication system such as Global System for Mobile communications (GSM), Universal Mobile Telecommunication System (UMTS) and Code Division Multiple Access (CDMA)) and an unlicensed wireless system (Wi-Fi or Bluetooth) have been built using separate networks that overlap with each other in some places. An unlicensed wireless system and a licensed wireless system both have their respective advantages and disadvantages. For example, the unlicensed wireless system provides a high speed service at a low cost and supports a narrow service area and low mobility. A licensed wireless system provides a low speed service at a high cost and supports a wide service area and high mobility.
Recently, unlicensed mobile access (UMA) technologies have been developed as a convergence means that combines a licensed wireless system and an unlicensed wireless system together for internetworking. Multi-mode mobile stations capable of connecting to both a licensed wireless system and an unlicensed wireless system also have been developed.
In UMA, a UMA network controller (UNC) can transparently provide a multi-mode mobile station with voice, data, and other services of a mobile communication system through an access point (AP) of an unlicensed wireless system such as a wireless local area network (WLAN) without modification of equipment of the mobile communication system such as a mobile switching center (MSC), serving GPRS support node (SGSN), and home location register (HLR).
UMA enables a mobile subscriber to use the same services as a licensed wireless system but through an unlicensed wireless system, such as Wi-Fi or Bluetooth. In addition. UMA enables a mobile network operator to remove shadow areas and extend service areas at a low cost by installing fixed Internet Protocol (IP) networks and WLAN access points at shadow areas, such as homes. Thus, the mobile network operator may realize a profit by encouraging replacement of wired telephones at home with mobile stations.
UMA is based on specifications created by a consortium of radio infrastructure builders, handset manufacturers, and network operators. UMA enables mobile subscribers to receive seamless voice and data services using their multi-mode mobile stations. UMA supports voice call and data session handover between a licensed wireless system and an unlicensed wireless system, thereby enabling seamless roaming and uninterrupted services.
As described above, compared with a licensed wireless system, an unlicensed wireless system provides services at a higher rate, has a narrower service area, and supports a smaller number of subscribers connectable to a base station. Hence, while a user of a mobile station moves between coverage areas of a licensed wireless system and unlicensed wireless system, an increased number of transitions between the licensed wireless system and unlicensed wireless system can be expected. Accordingly, it would be nice to provide an efficient handover mechanism for a combined communication system of a licensed wireless system and unlicensed wireless system.